The present invention relates generally to the delivery of bare die for placement onto printed circuit boards during the assembly process and more specifically, a method and apparatus for concurrently removing, inverting and transporting flip-chips from a semiconductor wafer to an automated pick-and-place machine for subsequent placement onto a circuit board substrate. More particularly, the invention relates to the accelerated throughput of the direct bare die feeding process which performs the function of removing known to be good die from a sawed wafer disposed on a adhesive coated film, inverting, so as the active surface is downward, and subsequently conveying to a distal pick-up location that is accessible to the assembly machine.
The present invention is an improvement of the throughput characteristics of a die extracting and delivery system associated with automated pick and place equipment, particularly those systems requiring the extraction, flipping and placement of numerous die or components at high speeds. It can be appreciated that methods for removing and delivering bare die from a wafer have been in use for many years. The present invention includes, among other aspects and features, a novel method for tandem handling of a multitude of die employing a linear array of vacuum nozzles for buffering, transferring and transporting the die.
Typically, the method for delivering bare die in the production of printed circuit boards (PCB), is to use a conventional tape and reel feeder whereby the bare die are xe2x80x9cprepackagedxe2x80x9d by first removing them from the wafer and predisposing them within a linear strip having pockets equidistantly embossed therewithin and covered by a thin film or cover tape. Alternative means would include placing the die into a matrix tray which has been portioned for each die. The primary concern with traditional methods for delivering bare die is the costs and reliability associated with placing the die into the embossed tape and then having to remove the flip-chip and discard the cover and pocket tape as waste during the assembly process. The preferred method to this double handling would eliminate the pre-packaging of the die by extracting the die directly from the wafer, placing it onto a conveyance means and presenting the die directly to a placement machine. An example of such a direct die feeder is shown in U.S. Pat. No. 6,173,750 issued to Davis et al, as well as U.S. Pat. No. 5,671,530 issued to Combs et al. These patents disclose an apparatus that removes die from a vertically oriented wafer and presents the die for subsequent placement onto a PCB. Because the referenced Davis patent is intended to replace the traditional tape feeders mentioned above, it is designed to interface to the placement machine as if it were a standard tape and reel feeder.
The present invention is considered a further improvement to a direct die from wafer feeder used with automated pick-and-place equipment, particularly those systems requiring the manipulation and placement of numerous die at high speeds. The present invention includes, among other aspects and features, a novel means for holding, turning over, and parallel queuing of die or flip-chips using a multitude of vacuum ports and a rotatable picking member.
There are numerous methods of attaching a die to the substrate of a PCB. The most common method is to bond wires to the upward facing circuit of a die that has been previously placed and affixed to the substrate. Electrical connections are thereby facilitated with the xe2x80x9cbondingxe2x80x9d of wires to pads on the exposed surface of the die to corresponding contacts on the substrate. In an alternative method, solder bumps are placed on the die circuit and then the die is turned over or xe2x80x9cflippedxe2x80x9d so as the solder bumps are aligned with corresponding pads on the substrate. The mechanical and electrical connections are accomplished by melting the solder bumps within an oven. The process is well known in the art as a controlled-collapse chip connection, or simply the C-4 process. It is a common practice in the industry to refer to a flip-chip as a bumped bare die or chip, the term xe2x80x9cflipxe2x80x9d is appended to chip in as much as the bare die must be turned over during the delivery process so as the circuit side of the flip-chip contacts the PCB. In this specification the term xe2x80x9cdiexe2x80x9d is used prior to turning the chip over, at which time the term flip-chip will generally be used.
The Davis U.S. Pat. No. 6,173,750 has an inherent maximum throughput governed by the concatenated steps of; (1) extracting, (2) flipping and (3) depositing onto the shuttle one die at a time. Furthermore, in the prior art, transference of the die from the wafer occurs only when the die shuttle is in the re-fill or loading position, hence when the shuttle is in the distal export location and waiting for the placement machine, the die extraction activity must remain in a wait state. Therefore, the inability to multiplex the xe2x80x9cdie picking from the wafer processxe2x80x9d with the xe2x80x9cdie delivery to the placement machine processxe2x80x9d significantly limits throughput. Accordingly the motivation for the present invention relies on the requirement to concurrently perform these operations, thusly providing flip-chips at a rate that is synchronous with the cycle time of the placement machine.
The present bare die feeder apparatus may not be as suitable for accelerated throughput requirements associated with circuit boards having a relatively high flip-chip component population, such as is the case with cell phones and similar miro-electronic devices. The metric for capacity is generally considered to be the total components which can be placed in a unit of time. Therefore the feeder cycle time is a function of the total number of feeders on the machine divided into the rated capacity of the placement machine. In the case of a multi-head placement machine the placement rate may often exceed the die feeder delivering throughput capabilities and accordingly the assembly process is required to enter a wait cycle that compromises productivity and thereby increases the overhead.
In these respects, the method for rapid bare die removal from a wafer according to the present invention is considered to be an improvement over the conventional concepts and designs of the prior art, and in so doing provides for an apparatus primarily developed for the purpose of the accelerated delivery of die as they are co-processed and queued for subsequent placement.
The present invention is directed towards a dual stage approach whereby flip-chips are removed from a wafer concurrently with the flip-chips being presented for placement. As described herein, one embodiment of the present invention is directed toward buffering the flipped-chips while the shuttle is being unloaded by the placement machine
In view of the foregoing limitations inherent in the known types of methods for delivering bare die now presented in the prior art, the present invention provides a new method for concurrent bare die removal from a wafer containing a plurality of flip-chips wherein a multiplexed or timeshared co-processing method can be utilized for the rapid throughput of die as they are removed from the wafer for subsequent placement.
The general purpose of the present invention, which will be described subsequently in greater detail, is to provide a new method for accelerating the die removal from a wafer that has many of the advantages of the method for delivering bare die mentioned heretofore and a novel feature that results in a new method for accelerated flip-chip delivery from a wafer which is not anticipated, rendered obvious, suggested, or even implied by any of the prior art method for delivering bare die, either alone or in any combination thereof.
To attain this, the present invention generally comprises a die acquisition station member, containing a nozzle, a die intermediate transfer station, containing a number of nozzles and a conveying method, such as a shuttle, which translates flip-chips placed on nozzles to a pick-up point. The acquisition member contains a nozzle having a suction port therein whereby a bumped bare die is secured as it is extracted and acquired from the wafer. A die intermediate transfer station has a quantity of nozzles, at a uniform pitch, whereby each nozzle retains a die as they are accumulated from the die acquisition member and waiting to be loaded onto the shuttle. This linear array of nozzles within the intermediate transfer station serves as a buffer to retain the die while the shuttle is away presenting die at the distal pick point. The shuttle also has a plurality of corresponding nozzles, with vacuum ports, orientated so as to be in direct alignment with the die transfer nozzles so that a group of flipped die can loaded in parallel from the nozzles of the transfer member onto the nozzles of the shuttle. This loading of the predisposed flipped die from the die transfer station onto the shuttle platform allows for the instantaneous and parallel loading of a group of flipped die onto the shuttle nozzles. Therefore, die subsequently migrate from the wafer as they are transitioned from the pick nozzle by releasing from the first plane and securing on the second plane by the die transfer station. Pneumatic flow valves enable the release and transfer of the flipped die from the wafer to the die transfer station, as well from the die transfer station to the shuttle. The die transfer station, having a multiple of nozzles, enables more than a single die to be picked and then retained while the shuttle is in the distal delivery position. This multi-nozzle die buffer array within the die transfer station offers a significant enhancement to the throughput capabilities by multiplexing the picking function with the presentation of flipped die to the placement machine.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof may be better understood, and in order that the present contribution to the art may be better appreciated. There are additional features of the invention that will be described hereinafter.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of the description and should not be regarded as limiting.
A primary object of the present invention is to provide a method for increasing the rate of throughput of bare die that have been removed from a wafer and turned over. This invention will serve to overcome the identified limitations inherent to the prior art of record.
An object of the present invention is to provide a method for rapid bare die removal and flipping from a wafer in order to provide die delivery cycle times that are capable of being synchronized with the high speed placement machines now available.
Another object is to provide a method for rapid bare die handling from a wafer that is capable of multiplexing the steps required for die extraction from the wafer.
Therefore the primary object of this patent is to provide a method for the accelerated bare die removal from a wafer that will improve the overall throughput and die availability and accordingly will serve to coordinate the feeder with the placement machine, exclusive of halt routines encountered when the demand for flip-chips exceeds the die delivery capabilities.
Other objects and advantages of the present invention will become obvious to the reader and it is intended that these objects and advantages are within the scope of the present invention.
To the accomplishment of the above and related objects, this invention may be embodied in the form illustrated in the accompanying drawings, attention being called to the fact, however, that the drawings are illustrative only, and that changes may be made in the specific construction illustrated.